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As described here, there is an API method for doing that in the YouTube Data API.
The documentation describes a method of forming an XML text format that automatically adds a video to your Watch Later playlist.
It will not work for you out of the box but with some moderate programming experience you (or someone else) should be able to make an application ...

You may be signed into multiple Google accounts. Google will use your "primary" Google account (typically the one you signed into first) as the account to use for liking, disliking, commenting and adding to "Watch Later" lists.

I just found out a method that is much easier and works 100% of the time! In your browser go to your Watch Later playlist and click the menu (the three dots in the right top corner) and add to playlist. Create a new playlist and name it something easy (I named it WL for example). Now go to that playlist and go to the same menu and instead of adding it to ...

I'm not aware of a way of doing this via the youtube UI (website). However you might be able to use the Youtube API. Access to the watch later list was introduced only in v2 of the API, v3 should also work. Note that since it's a private playlist you can only access it via an authenticated request.

I am not exactly sure but it depends on how the particular video is embedded from YouTube. You will see videos embedded in various different ways and dimensions.
Some videos are available for viewing at 240p while watched in YouTube but not when you watch the same video through some other site where it is embedded.
There is no such setting which makes the ...

Looks like it's just a bug.
If I look at all my lists (in a row across the top of you YouTube account) it shows View Later as being empty. If I click on the view list hyperlick below it though,I get the list with the recently added videos.

I've set it up to work almost like that.
Since Google shut down the YouTube subscription RSS feed it's a bit more work.
What I do is first grab the RSS feed for a channel I want to subscribe to.
The URL for a YouTube channel RSS feed is:
http://gdata.youtube.com/feeds/base/users/USER_NAME/uploads
Then I create a new IFTTT recipe and add a feed with the ...